Pyrimidine, also known as 1,3-diazobenzene, is a heterocyclic compound with the chemical formula C4H4N2. Pyrimidine is formed by substituting 2 nitrogen atoms for 2 carbons in the meta-position of benzene. It is a diazine and retains its aromaticity. Derivatives of pyrimidine widely exist in organic macromolecular nucleic acids, and many drugs also contain pyrimidine rings. In nucleic acids, three nucleobases are pyrimidine derivatives: cytosine, thymine and uracil. There are a variety of pyrimidine-containing drugs on the market, most of which are kinase inhibitors.
The two N atoms in Benzothiadiazole could possibly form intermolecular hydrogen bonding, leading to a more planar backbone. Benzothiadiazole is a strong electron-accepting molecular fragment. By fusing it with thiazole donor-acceptor dyes, near-infrared fluorescence was created. The benzothiadiazole ring is a useful n-type building block for designing electron-transport materials for organic and polymer light-emitting diodes (LEDs). Arene- and heteroarene-fused thiadiazoles have also found use in the design of low-band-gap materials for the construction of organic field-effect transmitters (OFETs), as stable organic radicals, and as one or two photon-absorbing materials for the design of nonlinear near-infrared (NIR) dyes. Benzothiadiazoles acting as the electron-accepting cores have been incorporated into dendrimer-type light-harvesting materials.